Enamel coated article



E/\/ r025 M ROWN M. BROWN EI'AL ENAMEL COATED ARTICLE Original Filed May 20, 1939 April 1946.

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- the alloy layer,

Patented Apr. 23, 1946 ENAMEL COATED ARTICLE Morris Brown, Western Springs, and Russel E. Harr, Downers Grove, Ill., assignors to Western Electric Company, N. Y., a corporation Original application Ma 274,750. ,Divided and this Incorporated, of New York y.20, 1939, Serial No.

1944, Serial No. 539,283

Claims. (Cl. 204-38) This invention relates to enamel coated articles and to methods of making enamel coated articles, and this application is a division of our copending application Serial No. 274,750, filed May 20,

1939, Patent 2,377,321 granted June 5, 1945.

Objects of the invention are the production of articles having a highly ornamental and serviceable enamel coating, and the provision of efflcient and economical methods for making such articles.

The invention is particularly adapted to the production of enameled articles such as the number plates which are incorporated in telephone dials. These plates comprise a metal base with a coating of vitreous enamel on the portions of the base that are exposed in the dial assembly. A highly adherent enamel coating is required to withstand rough usage and it is especially desirable to providea particularly smooth, even and unbroken surface on the enamel. The plates are often exposed to dirt-laden atmospheres in service and under these conditions even minute imperfections in the enamel surface may accumulate dust, dirt, lint and the like. These foreign materials are difilcult to remove from surface cracks and, pits, and the plate very soon becomes unsightly if any of these defects are present. Certain types of'number plates receive a multi-color finish in which variously colored enamels are applied successively and fired after the application of each color. Under this practice, the repetitive firing tends to develop surface defects or to aggravate defects in previously matured enamel.

In one embodiment of the invention, an improved number plate having an adherent and unpitted enamel coating is produced by forming a base from inexpensive sheet iron, copper plating the base, electrodepositing on the copper a uniform layer of nickel alloyed with a metal selected from the group consisting of iron, cobalt and manganese, applying a vitreous enamel on firing the base to fuse the enamel, applying a second enamel of contrasting color on portions of the fused enamel, and refiring the base to mature the second enamel.

A more complete understanding of the invention may be had by reference to the following detailed description taken in conjunction with the accompanying drawing, in which Fig. 1 is a plan view of a number plate .embodying the the invention, and

Fig. 2 is an enlarged sectional view of the number plate taken on the line 2-2 of Fig. 1.

In the first operation for producing a number plate in accordance with this invention, a ring or Sumcient sulphuric acid, is added to keep theso- I New York,

application June 8,

base It is formed from sheet metal. Various rades of iron or steel are suitable for this urpose and the material is selected primarily on the basis of cost and formability.

After the ring-shaped base cleaned by the usual methods and then completely coated with a layer of copper II. The copper can be applied conveniently in a conventional copper-cyanide electroplating process and a coating weight around 20 milligrams per square inch is generally satisfactory.

In the next operation an alloy I2 is applied over the copper in a uniform layer. Three types of alloy are suitable and good results alloying nickel with iron, or cobalt, or manganese.

If anickel-iron alloy is used, the iron content shouldbe between .50% and10.0% with the balance nickel and the best results are secured with an alloy having an iron content around 1.50%. This optimum composition can be obtained from an aqueous electroplating bath containing the following ingredients and operated under the following conditions:

Composition of bath Ounces per gallon of solution Nickel sulphate--- 24.0 Sodium chloride 3.0 Boric acid 4.0 Ferrous sulphate .0666

lution in a slightly acid condition, a pH of 5 being satisfactory. The process is operated cold at a current density around 10 amperes per square foot of cathode surface. Since a variationof this currenty density will aflect the proportions of iron in the deposited alloy for the given solution and temperature, it is necessary to consider, this interrelation of position for different solution concentrations and operating temperatures. The ferrous sulphate can be added as such to initiate the process and then maintained by placing pure iron anodes in parallel with pure nickel anodes in the bath.

If the nickel is alloyed with cobalt, a cobalt content between 1.0% and 15.0% is operable and a cobalt content of 5.0% is preferred. If a nickelmanganese alloy is employed, the manganese percentage is held between 20% and 5.0%, and 1.0%

manganese is optimum. The nickel-cobalt and is formed, it is are obtained by current density and alloy com-' metals, corresponding to the elements employed for electrodepositing the nickel-iron alloy,. as above described.

After the copper and the alloy coatingshave been deposited, the base is ready to receive the enamel which is applied only on the face or the ri The enamel is restricted to the face of the ring, which is the portion exposed in service, in order to minimize the cost of the article and also to facilitate the maintenance of over-all dimensional tolerances.

istics are preserved during retiring operations and are reflected in all portions of the completed enamel coating. For most applications, a coating weight of 20 milligrams per square inch for both the copper and the alloy is satisfactory. It may be desirable to vary these values somewhat for different enamel compositions and, in general, the copper and alloy layers should be of about A coating of white enamel 13. such .as a lead bore-silicate enamel opacifled with arsenic oxide, is applied first. The enamel is distributed on'the alloy surface. either in the form of dry powder or by a wet process in which the enamel particles are mixed with water and a flotation agent, such as clay. The base is then fired at 1600 F. for four and one-half minutes to fuse the enamel.

Identifying characters in contrasting colors areusually required to complete the plate. One type of plate, shown in the drawing, has a background l4,'letters l5 and numerals l6. These characters are produced with an inkyisuspension of colored metallic oxides or frits in a vehicle such as linseed oil and'are applied on the surface of the white enamel by a printing operation. The background, which may be blue or black, is ap lied first and the plate is then baked at about 300 F.

to harden the ink so that it will not be marred in subsequent p ting operations. Th letters,

equal weight.

The combination of copper and alloy layers also adequately protects the portions of the base that are not covered with enamel againstatmos alloy comprising from 1.0% to 15.0% cobalt and the balance nickel and being substantially the which are usually black, are then applied and the plate is then again baked at a temperature of about 300 F. The numeral are usually colored red and are applied in the same manner, after which the entire "plate is again fired tofully mature the ceramic ink which requires a temperature around l3 00 F. for approximately 4.5

minutes.

The resultant enamel coating is highly adherent.

and all portions thereof havea smooth, continuous'surfalce that does not tend to accumulate foreign materials. In this type .of product, pitting. of the enamel is a serious source of trouble. The

occurrence of very small pits is not easily de-' tected when the plates are new, but after a period of service. dirt and other foreign particles tend to accumulate andbeconie imbedded in the pits to form smudges. These smudges are very dimcult to remove. particularly becausethe number plates are not readily accessible for cleaning after they are assembled in a dial. Use of the described combinations of copper and alloy undercoatings prevents the formation of pits in the enamel. The initially applied enamel i smooth, glossy andfree of pits and these desirable surface charactercomprising substantially 5.0% cobalt and the balsame thickness as the copper plate, and a fused enamel coating over the nickel-cobalt alloy.

. 2. In an enamel coated article, a ferrous base, a-copper coating on the base, a layer of nickel- -cobalt alloy comprising from 1.0% to 15.0% cobalt and the balance nickel on the copper, and

a coating of fused enamel on the alloy.

3. In an enamel coated article, a ferrous base, a copper plate on the base, a nickel-cobalt alloy ance nickel on the copper plate, and a vitrified enamel on the alloy. v r 4. In a method of forming an article, the steps of electrodepoeiting a copper coating on aferrous metal basamlectrodeposlting a nickel-cobalt comprising 5.0% cobalt and the balance nickel on he c pp r. applyin a vitreous enamel to the coated base, and firing the article-to. fuse the enamel and form an enameled coating.

5. A method of making an-enamel coated article which com rises plating a copper coating of predetermined weight on a fellow metal base,

electrodepositing a layer of nickel-cobalt alloy of substantially 5.0%. cobalt and the balance nickel on the copper plating, and applying a vitreous enamel coating over the alloy layer.

Mortars BROWN. RUSSEL E. HARR. 

